Field of the Invention
The present invention relates to metal oxide based memory devices and methods for manufacturing such devices; and more particularly to memory devices having data storage materials based on metal oxide compounds fabricated with a biased plasma oxidation process which improves the interface between the memory element and a top electrode for a more uniform electrical field during operation, which improves device reliability.
Description of Related Art
Resistive random access memory, RRAM or ReRAM, is a type of nonvolatile memory that provides the benefits of small cell size, scalability, ultrafast operation, low-power operation, high endurance, good retention, large On/Off ratio, and CMOS compatibility. One type of RRAM includes a metal oxide layer than can be caused to change resistance between two or more stable resistance ranges by application of electrical pulses at levels suitable for implementation in integrated circuits, and the resistance can be read and written with random access to indicate stored data.
RRAM memory may include a metal oxide memory element in a current path between first and second electrodes. The electrodes may be terminals to access devices and/or may be coupled to access lines such as bit, word, and source lines. The access lines are connected to circuitry to perform operations, such as SET and RESET operations, which may operate to change the state of the memory element in order to store data.
In prior methods of forming a memory element of an RRAM memory cell, a metal plug, such as a tungsten plug, is deposited using chemical vapor deposition (CVD). The tungsten plug is oxidized through rapid thermal oxidation. This oxidation process creates a layer of metal oxide that is the memory element of the memory cell. A top electrode material electrode is deposited onto this oxidized surface. However, the oxidized surface created by this oxidation process is rough, which may result in a non-uniform electrical field during operation and affect device reliability. Further, the resulting memory cells fabricated with this process have a relatively low resistance, and the consistency of resistance from cell to cell is low, and therefore the cells in a single device have a wide range of resistances.
It is therefore desirable to provide a memory cell and method of manufacture that provides a uniform electrical field during operation. It is further desirable to provide a memory cell and method of manufacture that has increased cell resistance and improved consistency of resistances with other memory cells within a device.